text: In internal combustion engines, the time area integral is considered over the range of valve opening. The time lift integral is given by
  where  is the time per revolution,  is the distance from the camshaft centreline to the cam tip,  is the radius of the camshaft (that is,  is the maximum lift),  is the angle where opening begins, and  is where the valve closes (seconds, mm, radians). This has to be factored by the width (circumference) of the valve throat. The answer is usually related to the cylinder's swept volume.